1. Field of the Invention
The present invention generally relates to a communication system, and more particularly, to a method of indicating a type of a target evolved Node B (eNB) to a core network so that the core network can locate a proper gateway and control a user.
2. Description of the Related Art
A system structure of a System Architecture Evolution (SAE) is illustrated in FIG. 1.
User Equipment (UE) 101 is a terminal device for receiving data. Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN) 102, also referred to as an eNB, is a radio access network of an Long Term Evolution (LTE) SAE, for providing an interface through which an LTE mobile device may access the radio network. EUTRAN 102 is connected to a Mobility Management Entity (MME) 103 and a user plane entity Serving Gateway 104 through the interface S1. MME 103 is for managing UE's mobile context, session context, and storing the user information on security. Serving Gateway 104 primarily provides a function of a user plane. The interface S1-MME is for establishing a radio access bearer for the UE 101, and forwarding messages from UE 101 to MME 103 through a wireless access network.
The combined function of MME 103 and Serving Gateway 104 is similar to that of an original General Packet Radio Service (GPRS (SGSN Supporting Node) 106. It is possible that both MME 103 and Serving Gateway 104 could be located in the same physical entity. PDN Gateway 105 is for performing the functions such as accounting, legally monitoring, etc. It is possible that both the Serving Gateway 104 and the PDN Gateway 105 could be located in the same physical entity. SGSN 106 provides routing for data transmission in an existing UMTS. The existing SGSN 106 finds corresponding Gateway GPRS Supporting Nodes (GGSN) according to an Access Point Name (APN). HSS 107 is a home subscription sub-system of the UE 101, for storing user information such as the UE's 101 current location, the serving node's address, user's security related information, UE's 101 active Packet Data Protocol (PDP) context, and so on. PCRF 108 provides a Quality of Service (QoS) policy and accounting rules through the interface S7.
In general, the user data stream reaches the Serving Gateway 104 through PDN Gateway 105. Then, through the GPRS Tunnel Protocol (GTP) channel, data is sent by the Serving Gateway 104 to the eNB in which the UE 101 is located, and then sent by the eNB to corresponding UE 101.
Evolved Packet Core (EPC) is an LTE core network. In this case, each eNB is connected to several MMEs in an MME pool. Each eNB is connected to several Serving GateWays S-GWs in S-GW pool. The interface between eNBs is referred to as an X2.
In an enhanced network architecture, a new eNB, i.e., HeNB, is defined. HeNB refers to a Node B applied in a home. It also can be applied in sites such as a university, a company and so on. An HeNB is a Plug-and-Play device. The difference between an HeNB and a common macro eNB lies in that usually not all UEs can access the HeNB. For example, only the UEs in a user's home or the ones authorized to access the HeNB can access the corresponding HeNB.
For the HeNB in a company, only the company's staff and authorized partners can access the HeNB. The HeNB group (e.g., the HeNB in a company) bearing the same access subscriber cluster is referred to as a Closed Subscriber Group (CSG). In an HeNB system, each CSG has a unique IDentifier (ID) for identifying the CSG. This ID can be broadcast through the broadcast channel. The CSG ID is included in Common Gateway Interface (CGI) (cell unique ID).
For example, all HeNBs can be divided into three categories, that is, the eNB in a home, the eNB in a small corporation, and the eNB in large corporation. The CGI is made up of 28 bits in total. If the HeNB is an eNB in a home, the first 27 bits in the CGI indicates the CSG ID, and the last bit indicates that the HeNB is an eNB in a home. If the HeNB is an eNB in a small corporation, the first 24 bits in CGI indicates the CSG ID, the last two bits indicate that the corporation is small-scaled, and the remaining two bits stand for the eNB. In a home, one eNB corresponds to one CSG with unique CSG ID. While in a corporation, a plurality of eNB s can simultaneously correspond to one CSG. Therefore, the same CSG ID is broadcast by a plurality of eNodeBs. An HeNB can be connected to the HeNB gateway, and the HeNB gateway is connected to the core network.
A UE can access a plurality of CSGs. The IDs of these CSGs form a CSG white list of the UE. The UE restores its white list. In addition, the core network or the operation and maintenance center should know the UE's white list.
In the following description, an HeNB is referred to as Home Node B (HNB), including the home station deployed in the enhanced systems. An HNB gateway is referred to as GW or HNB GW.
Conventionally, when a UE moves between macro cells, the UE sends a measurement report to the source cell, including measurement results on signal quality for a group of adjacent cells. According to the measurement report, the source cell determines to switch the UE to the cell with better signal quality. If no interface X2 exists between the source cell and the target cell, the switch is implemented through interface S1. The switch processing implemented through interface S1 is illustrated in FIG. 2.
In step 201, the UE sends the measurement report message to the source eNB, including scrambled codes applied in the target cell step 202, according to the measurement report message, the source eNB determines to switch the UE to an adjacent cell with better signal quality. The adjacent cell is a macro cell. The source eNB sends a switching requirement message to MME, including an eNB UE SLAP ID allocated by eNB to the UE, a target macro eNB ID, and packets transparently transferred from the source eNB to the target eNB. The target macro eNB ID is included in the CGI. According to the information included in the measurement report in step 201, the source eNB can obtain the target eNB ID. In step 203, by the target macro eNB ID included in the message in step 202, MME locates the target eNB and then sends a switching request message to the target eNB, including the MME UE S1AP ID allocated to UE by the MME, information on the to-be-established SAE bearer such as an SAE bearer ID, a transmission layer address and QoS information. The message further includes the packets transparently transferred from the source eNB to the target eNB. In step 204, the target eNB prepares resources and sends a switching request response message to MME, including information on the SAE bearers that can be established, information on the SAE bearers that can not be established, and the packets transparently transferred from the target eNB to the source eNB. In step 205, the MME sends a switching command message to the source eNB, including information on the SAE bearers that can be established, information on the SAE bearers that can not be established, and packets transparently transferred from the target eNB to the source eNB. In step 206, the source eNB sends a channel reconfiguration request message to the UE. In step 207, UE sends a channel reconfiguration response message to the target eNB. In step 208, the target eNB sends a switching notification message to the source MME. In step 209, MME sends a UE context release command message to the source eNB. In step 210, the source eNB sends a UE context release complete message to the MME.
According to previous description, not all UEs can access the target cell if the target cell is an HNB. Therefore, it is preferable that the MME determine whether the UE is allowed to access the target eNB or not. If not, the MME can directly reject this switching.
In another aspect, if the target cell is an HNB that is connected to the core network through the GW, it is necessary for the MME to locate the corresponding GW according to the message of step 202.
As described above, in the conventional art, when the source eNB sends the switching requirement message to the MME, the source eNB does not include the type of the target Node, but only the target eNB ID in the message. Therefore the MME has no idea where the macro eNB or the HNB are switched. If the MME does not know the type of the target eNB, the MME can not implement subsequent operations according to the type of target eNB. For example, if the target eNB is an HNB, it is necessary for the MIME to locate the GW for the target eNB, and for a macro eNB, the MME can directly locate its position. In another aspect, if the MME knows that the target eNB is an HNB, the MME can act as an access controller for UE.